Use TXT
When people primarily read the content and its internal structure is intentionally informal.
Family 01
Text & data
A file can be text without being self-describing. Encoding, grammar, delimiters, and line-ending conventions are separate questions.
| Format | Identity | Good fit | Watch for |
|---|---|---|---|
| Plain text .txttext/plain | No required file signature. Character encoding is separate metadata or an agreement between producer and reader. | Notes, source-like content, logs, and data intended to remain readable with minimal tooling. | Encoding and line endings may be ambiguous. “Text” does not define a record structure. |
| JSON .jsonapplication/json | A Unicode text serialization with objects, arrays, strings, numbers, booleans, and null. Interoperable exchange uses UTF-8. | Structured data where explicit names and nested values matter. | The standard grammar has no comments or trailing commas. Duplicate object names produce unpredictable interoperability. |
| CSV .csvtext/csv | Delimited records. RFC 4180 documents a widely used comma-separated form, but real-world dialects vary. | Flat tables that should move easily between spreadsheets, databases, and scripts. | Delimiter, encoding, header presence, decimal convention, and formula interpretation may differ by tool. |
Selection notes
Choose based on the structure you need to preserve, not on which extension is easiest to type.
Use JSON
When names, nested values, and predictable programmatic parsing are more important than compact tables.
Use CSV
When the data is genuinely rectangular and both sides agree on dialect and encoding.